In order to meet the demand of high density, high transmission rate, reduction of component size, and high production scalability, the development of the Planar Lightwave Circuit (PLC) and related waveguide packaging is undoubtedly the trend in the optical networking industry. Optical fiber arrays are used for the connection of light input/output ends of optical fibers to the waveguide substrate. Since the alignment accuracy for the above connection is down to the submicron level, the fabrication of the optical fiber array is crucial to achieve and maintain the high production yield of PLC devices. Moreover, to increase the density and reduce the size of the waveguide, efforts are made to reduce the waveguide pitch and thus the inter-fiber pitch of the fiber array down to 127 μm which is about half of the standard-type waveguide pitch of 250 μm.
A standard-type full-pitch optical fiber array 100 is shown in FIG. 1. It generally comprises a lower V-groove substrate 101, a cover lid 102 and optical fibers 103. Ultraviolet-(UV-) or thermal-curable adhesive 105 is used for fixing a bare end of the optical fibers 103 into V-shaped grooves of substrate 101. UV-curable adhesive 106 is used for fixing ribbon fibers 104 onto the V-groove substrate 101. However, the bonding surface at interface 107 between ribbon fibers 104 and V-groove substrate 101 is very thin. Consequently, the adhesion at interface 7 is very weak. Especially for high-channel optical fiber arrays (more than 16 channels/fibers), it is very easy to cause failure at the interface 107 when subjected to a side pull test.
An example of a conventional half-pitch fiber array 200 is shown in FIG. 2. A ribbon fiber housing lid 210 is fixed to a lower V-groove substrate 208. Ribbon fibers 211a and 211b, which are arranged in two stages, are inserted through a housing groove 212 formed in the ribbon fiber housing lid 210 so that the upper and lower fibers are alternatively aligned in the V-shaped grooves. Then, an upper cover lid 209 is fixed to the lower V-groove substrate 208 therein to form the optical fiber array 200. Normally, UV- or thermal-curable adhesive 213 is used for fixing bare fibers 214a and 214b into V-shaped grooves of the lower V-groove substrate 208, and for fixing of ribbon fibers 211a and 211b inside a housing groove 212. In this configuration of a half-pitch fiber array, the ribbon fiber housing lid 210 can improve the side pull strength when compared to the case of using only a single drop adhesive 106 as shown in FIG. 1. However, the adhesion of interface 215 is still relatively weak because there is only a very thin layer of adhesive 213 at the interface 215 between ribbon fibers 211b and the V-groove substrate 208. Moreover, in order to reduce the bending loss of bare fibers 214a and 214b, the length, shown as “d,” of ribbon fibers 211a and 211b inside the housing groove 212 is generally quite short (typically around 4 mm). As a result, when the fiber array 200 is subjected to a side pull test, cracks may initiate in the interface 215 and may propagate to the bare optical fibers 214a and 214b. This may further break the bare optical fibers 214a and 214b and degrade or ruin system performance.
Related prior art patents that suffer from this or other limitations are shown in U.S. Pat. No. 6,231,244, issued to Fukuyama et al.; U.S. Pat. No. 6,160,937, issued to Fukuyama et al.; and U.S. Pat. No. 5,379,360, issued to Ota et al.; each of which is expressly incorporated herein by reference in their entirety.